If the system of equations
3x + y = a
2x + 5y = 2a
has a solution (x,y) when x = -2, compute a
We can rewrite the system of equations by replacing \(x\) with \(-2\) to get
Multiplying the first equation by \(2\), we have \(2y-12=2a\).
Subtracting this from the second equation says that \(3y+2=0\), so therefore \(y=-2/3\), and so \(a=-20/3\).